Done it before with NaNO3 added at 1 ppm per day along with ethanol dosing in an NPS tank. It is quite effective to lower PO4 concentration to undetectable.
Maybe it's just me, but setting up a bioball tower or rinsing out filter socks seems far less easy than just adding a couple drops of nitrate every day. GFO is nice of course but dosing nitrate can enhance PO4 removal.
If one uses filter socks...it is the less rinsing that will help increase nitrate(less interaction with the tank).
It really makes zero sense to dose something that your tank already is producing and processing.
Oh, what could be easier than a bioball tower...stick bioballs in the tank and your done.